Niinemets Ulo, Wright Ian J, Evans John R
Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Tartu, Estonia.
J Exp Bot. 2009;60(8):2433-49. doi: 10.1093/jxb/erp045. Epub 2009 Mar 2.
Foliage structure, chemistry, photosynthetic potentials (V(cmax) and J(max)), and mesophyll diffusion conductance (g(m)) were quantified for 35 broad-leaved species from four sites with contrasting rainfall and soil fertility in eastern Australia. The aim of the study was to estimate the extent to which g(m) and related leaf properties limited photosynthesis (A), focusing on highly sclerophyllous species typical of the 'slow-return' end of the leaf economics spectrum. Leaf dry mass per unit area (M(A)) varied approximately 5-fold, leaf life span (L(L)) and N (N(M)) and P (P(M)) contents per dry mass approximately 8-fold, and various characteristics of foliage photosynthetic machinery 6- to 12-fold across the data set. As is characteristic of the 'leaf economics spectrum', more robust leaves with greater M(A) and longevity were associated with lower nutrient contents and lower foliage photosynthetic potentials. g(m) was positively correlated with V(cmax) and J(max), and these correlations were stronger on a mass basis. Only g(m)/mass was negatively associated with M(A). CO(2) drawdown from substomatal cavities to chloroplasts (C(i)-C(C)) characterizing mesophyll CO(2) diffusion limitations was larger in leaves with greater M(A), lower g(m)/mass, and lower photosynthetic potentials. Relative limitation of A due to finite mesophyll diffusion conductance, i.e. 1-A(infinite g(m))/A(actual g(m)), was always >0.2 and up to 0.5 in leaves with most robust leaf structure, demonstrating the profound effect of finite g(m) on realized photosynthesis rates. Data from different sites were overlapping in bivariate relationships, and the variability of average values between the sites was less than among the species within the sites. Nevertheless, photosynthesis was more strongly limited by g(m) in low rain/high nutrient and high rain/low nutrient sites that supported vegetation with more sclerophyllous foliage. These data collectively highlight a strong relationship between leaf structure and g(m), and demonstrate that realized photosynthesis rates are strongly limited by g(m) in this highly sclerophyllous flora.
对来自澳大利亚东部四个降雨和土壤肥力不同的地点的35种阔叶树种的叶片结构、化学组成、光合潜力（V(cmax) 和 J(max)）以及叶肉扩散导度（g(m)）进行了量化。本研究的目的是评估g(m)和相关叶片特性对光合作用（A）的限制程度，重点关注叶经济谱“慢回报”端典型的高硬叶植物物种。单位面积叶干质量（M(A)）变化约5倍，叶寿命（L(L)）以及每单位干质量的氮（N(M)）和磷（P(M)）含量变化约8倍，整个数据集中叶片光合机构的各种特征变化6至12倍。正如“叶经济谱”的特征那样，具有更高M(A)和更长寿命的更坚韧叶片与更低的养分含量和更低的叶片光合潜力相关。g(m)与V(cmax) 和 J(max)呈正相关，并且这些相关性在以质量为基础时更强。只有g(m)/质量与M(A)呈负相关。在具有更高M(A)、更低g(m)/质量和更低光合潜力的叶片中，表征叶肉CO₂扩散限制的从气孔下腔到叶绿体的CO₂浓度下降（C(i)-C(C)）更大。由于叶肉扩散导度有限导致的A的相对限制，即1 - A(无限g(m))/A(实际g(m))，在具有最坚韧叶片结构的叶片中始终>0.2且高达0.5，这表明有限的g(m)对实际光合速率有深远影响。来自不同地点的数据在双变量关系中相互重叠，并且各地点之间平均值的变异性小于各地点内物种之间的变异性。然而，在支持具有更多硬叶植物的低雨/高养分和高雨/低养分地点，光合作用受g(m)的限制更强。这些数据共同突出了叶片结构与g(m)之间的紧密关系，并表明在这种高硬叶植物群中，实际光合速率受到g(m)的强烈限制。
